■ From Raw Story and the Observer (h/t MiroCollas via Twitter; my paragraphing and emphasis throughout):

Using instruments on earlier satellites, scientists could see that the area covered by summer sea ice in the Arctic has been dwindling rapidly. But the new measurements [made by the new CryoSat-2 satellite] indicate that this ice has been thinning dramatically at the same time.

For example, in regions north of Canada and Greenland, where ice thickness regularly stayed at around five to six meters in summer a decade ago, levels have dropped to one to three meters.

“Preliminary analysis of our data indicates that the rate of loss of sea ice volume in summer in the Arctic may be far larger than we had previously suspected,” said Dr Seymour Laxon, of the Centre for Polar Observation and Modelling at University College London (UCL), where CryoSat-2 data is being analyzed.

“Very soon we may experience the iconic moment when, one day in the summer, we look at satellite images and see no sea ice coverage in the Arctic, just open water.”

Being able to measure the area covered by Arctic ice gives us one metric. But being able to measure the thickness (as this new satellite does) gives us quite another.

Note those numbers above — from 5–6 meters just a decade ago, to 1–3 meters now. That’s a loss in volume from thinning of more than 50%, even if the area covered stayed the same — which it hasn’t.

“Since the 1970s, there’s been a 40% decrease in the summer sea ice extent,” said Jonny Day, a climate scientist at the National Centre for Atmospheric Science at the University of Reading, who led the latest study.

A 40% decrease in area (over 40 years) times a greater-than-50% decrease in thickness (in a decade) is a shockingly small number, even if the thickness changes aren’t uniform. The Raw Story article states:

[R]eductions in the volume of summer sea ice [have been] around 70% over the past 30 years.

Read it through carefully — there are some ifs and maybes in it regarding rate of change, including a semi-offsetting trend in winter ice.

But still, the summer data is real, the summer losses are real. I think we’ll certainly see ice-free Arctic summers in this decade.

We’ve been off on every estimate of global warming consequences I’ve seen; each has been too conservative compared to later measurements. I expect this be the same, to surprise us with its speed.

■ Another section of the same article illustrates a point I’ve made repeatedly about our current situation, namely:

Even if we stop right now, we still get 1.5°C (3°F) global warming by 2100. Half has occurred; half is in the pipeline, unavoidable.

This is what “half is in the pipeline” means, just so you know:

The consequences of losing the Arctic’s ice coverage, even for only part of the year, could be profound.

Without the cap’s white brilliance to reflect sunlight back into space, the region will heat up even more than at present. As a result, ocean temperatures will rise and methane deposits on the ocean floor could melt, evaporate and bubble into the atmosphere.

Scientists have recently reported evidence that methane plumes are now appearing in many areas. Methane is a particularly powerful greenhouse gas and rising levels of it in the atmosphere are only likely to accelerate global warming.

And with the disappearance of sea ice around the shores of Greenland, its glaciers could melt faster and raise sea levels even more rapidly than at present.

Professor Chris Rapley of UCL said: “With the temperature gradient between the Arctic and equator dropping, as is happening now, it is also possible that the jet stream in the upper atmosphere could become more unstable. That could mean increasing volatility in weather in lower latitudes, similar to that experienced this year.”

Permanent loss of summer Arctic ice is just one of the changes that’s unavoidably “in the pipeline.” But it illustrates the concept; we will get to 1.5°C (3°F) no matter what we do.

I’ve heard, by the way, that methane is a worse greenhouse gas than CO2. If so, this is one reason beef consumption is being discouraged by climatologists. The number of cows raised to feed a planetful of beef-eaters can produce a whole lot of methane.

World population is 7 billion humans. How many cows do you think are alive right now, producing atmospheric methane?

Combine the story above — that getting to 1½°C warmer is inevitable — with this story (do click; Obama gets a name mention), and I hope you can see where I’m headed with my own recommendation.

There really is only one choice; the others are almost not worth pursuing, since they all lead to the “do nothing” outcome.

Said differently, as I look at this problem, the answer is increasingly obvious. The only trick is getting there.